Merge list construction in triangular prediction

ABSTRACT

A method of video decoding in a decoder is described. A first syntax element in a coded video bit stream is received. The first syntax element indicates a maximum allowed number of merge candidates in a set of coding blocks. A maximum allowed number of triangular prediction mode (TPM) candidates for the set of coding blocks is set based on a second syntax element when the second syntax element is received, otherwise it is set based on the first syntax element. When a current coding block in the set of coding blocks is coded in a triangular prediction mode, a triangular prediction candidate list of the current coding block is constructed based on a number of TPM candidates. The number of TPM candidates on the triangular prediction candidate list is equal to the maximum allowed number of TPM candidates.

INCORPORATION BY REFERENCE

This present disclosure is a continuation of U.S. application Ser. No.16/528,019, filed Jul. 31, 2019, which claims the benefit of priority toU.S. Provisional Application No. 62/816,058, “Merge List Construction inTriangular Prediction,” filed on Mar. 8, 2019, which is incorporated byreference herein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described here is atechnique henceforth referred to as “spatial merge”.

Referring to FIG. 1, a current block (101) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (102 through 106, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide method and apparatus for videoencoding/decoding. In some examples, an apparatus includes processingcircuitry for video decoding.

According to an embodiment of the present disclosure, a method for videodecoding in a decoder is provided. In the method, a first syntax elementin a coded video bit stream is received. The first syntax elementindicates a maximum allowed number of merge candidates in a set ofcoding blocks in the coded video bit stream. A maximum allowed number oftriangular prediction mode (TPM) candidates for the set of coding blocksis set based on a second syntax element when the second syntax elementis received. Otherwise, the maximum allowed number of TPM candidates isset based on the first syntax element. When a current coding block inthe set of coding blocks is coded in a triangular prediction mode, atriangular prediction candidate list of the current coding block isconstructed based on a number of TPM candidates. The number of TPMcandidates on the triangular prediction candidate list is less than orequal to the maximum allowed number of TPM candidates.

According to an embodiment of the present disclosure, an apparatus forvideo coding is provided. The apparatus includes processing circuitry.The processing circuitry is configured to receive a first syntax elementin a coded video bit stream. The first syntax element indicates amaximum allowed number of merge candidates in a set of coding blocks inthe coded video bit stream. The processing circuitry is furtherconfigured to set a maximum allowed number of triangular prediction mode(TPM) candidates for the set of coding blocks based on a second syntaxelement when the second syntax element is received. Otherwise, theprocessing circuitry is configured to set the maximum allowed number ofTPM candidates based on the first syntax element. When a current codingblock in the set of coding blocks is coded in a triangular predictionmode, the processing circuitry is configured to construct a triangularprediction candidate list of the current coding block based on a numberof TPM candidates. The number of TPM candidates on the triangularprediction candidate list is less than or equal to the maximum allowednumber of TPM candidates.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform a method forvideo decoding. In the method, a first syntax element in a coded videobit stream is received. The first syntax element indicates a maximumallowed number of merge candidates in a set of coding blocks in thecoded video bit stream. A maximum allowed number of triangularprediction mode (TPM) candidates for the set of coding blocks is setbased on a second syntax element when the second syntax element isreceived. Otherwise, the maximum allowed number of TPM candidates is setbased on the first syntax element. When a current coding block in theset of coding blocks is coded in a triangular prediction mode, atriangular prediction candidate list of the current coding block isconstructed based on a number of TPM candidates. The number of TPMcandidates on the triangular prediction candidate list is less than orequal to the maximum allowed number of TPM candidates.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a current block and itssurrounding spatial merge candidates in accordance with H.265.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system (200) in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 6 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 7 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 8 shows an example of candidate positions from which a set of mergecandidates can be selected to construct a merge candidate list inaccordance with an embodiment.

FIG. 9 shows another example of candidate positions from which a set ofspatial merge candidates can be selected to construct an extended mergecandidate list in accordance with an embodiment.

FIG. 10 shows an example of candidate pairs on an extended merge listfor a redundancy check process in accordance with an embodiment.

FIG. 11 shows an example of deriving a temporal merge candidate on anextended merge list in a current picture in accordance with anembodiment.

FIG. 12 shows candidate positions from which a temporal merge candidateon an extended merge list can be selected in accordance with anembodiment.

FIG. 13 shows examples of partitioning a coding unit into two triangularprediction units in accordance with an embodiment.

FIG. 14 shows an example of spatial and temporal neighboring blocks usedto construct a uni-prediction candidate list for a triangular predictionmode in accordance with an embodiment.

FIG. 15 shows an example of a lookup table used to derive a splitdirection and partition motion information based on a triangle partitionindex in accordance with an embodiment.

FIG. 16 shows an example of a coding unit applying a set of weightingfactors in an adaptive blending process in accordance with anembodiment.

FIG. 17 shows an example of a coding unit applying another set ofweighting factors in an adaptive blending process in accordance with anembodiment.

FIG. 18 shows a flow chart outlining a triangular prediction modecandidate list construction process according to an embodiment of thedisclosure.

FIG. 19 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

I. Video Coding Encoder and Decoder

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an embodiment of the present disclosure. Thecommunication system (200) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (250). Forexample, the communication system (200) includes a first pair ofterminal devices (210) and (220) interconnected via the network (250).In the FIG. 2 example, the first pair of terminal devices (210) and(220) performs unidirectional transmission of data. For example, theterminal device (210) may code video data (e.g., a stream of videopictures that are captured by the terminal device (210)) fortransmission to the other terminal device (220) via the network (250).The encoded video data can be transmitted in the form of one or morecoded video bit streams. The terminal device (220) may receive the codedvideo data from the network (250), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (200) includes a secondpair of terminal devices (230) and (240) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (230) and (240)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (230) and (240) via the network (250). Eachterminal device of the terminal devices (230) and (240) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (230) and (240), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and(240) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (250) represents any number ofnetworks that convey coded video data among the terminal devices (210),(220), (230) and (240), including for example wireline (wired) and/orwireless communication networks. The communication network (250) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(250) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (313), that caninclude a video source (301), for example a digital camera, creating forexample a stream of video pictures (302) that are uncompressed. In anexample, the stream of video pictures (302) includes samples that aretaken by the digital camera. The stream of video pictures (302),depicted as a bold line to emphasize a high data volume when compared toencoded video data (304) (or coded video bit streams), can be processedby an electronic device (320) that includes a video encoder (303)coupled to the video source (301). The video encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (304) (or encoded video bit stream (304)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (302), can be stored on a streamingserver (305) for future use. One or more streaming client subsystems,such as client subsystems (306) and (308) in FIG. 3 can access thestreaming server (305) to retrieve copies (307) and (309) of the encodedvideo data (304). A client subsystem (306) can include a video decoder(310), for example, in an electronic device (330). The video decoder(310) decodes the incoming copy (307) of the encoded video data andcreates an outgoing stream of video pictures (311) that can be renderedon a display (312) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (304),(307), and (309) (e.g., video bit streams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can includeother components (not shown). For example, the electronic device (320)can include a video decoder (not shown) and the electronic device (330)can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to anembodiment of the present disclosure. The video decoder (410) can beincluded in an electronic device (430). The electronic device (430) caninclude a receiver (431) (e.g., receiving circuitry). The video decoder(410) can be used in the place of the video decoder (310) in the FIG. 3example.

The receiver (431) may receive one or more coded video sequences to bedecoded by the video decoder (410); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (401), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (431) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (431) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween the receiver (431) and an entropy decoder/parser (420) (“parser(420)” henceforth). In certain applications, the buffer memory (415) ispart of the video decoder (410). In others, it can be outside of thevideo decoder (410) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (410), forexample to combat network jitter, and in addition another buffer memory(415) inside the video decoder (410), for example to handle playouttiming. When the receiver (431) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (415) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (415) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstructsymbols (421) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (410),and potentially information to control a rendering device such as arender device (412) (e.g., a display screen) that is not an integralpart of the electronic device (430) but can be coupled to the electronicdevice (430), as was shown in FIG. 4. The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (420) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (420) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (420) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (415), so as tocreate symbols (421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). The scaler/inversetransform unit (451) can output blocks comprising sample values, thatcan be input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (458). The currentpicture buffer (458) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(455), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (452) has generated to the outputsample information as provided by the scaler/inverse transform unit(451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (451) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (457) from where themotion compensation prediction unit (453) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (453) in the form of symbols (421) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (457) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bit stream) and made available to the loopfilter unit (456) as symbols (421) from the parser (420), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (412) as well as stored in the referencepicture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (420)), the current picture buffer (458) can becomea part of the reference picture memory (457), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (410) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (410) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to anembodiment of the present disclosure. The video encoder (503) isincluded in an electronic device (520). The electronic device (520)includes a transmitter (540) (e.g., transmitting circuitry). The videoencoder (503) can be used in the place of the video encoder (303) in theFIG. 3 example.

The video encoder (503) may receive video samples from a video source(501) (that is not part of the electronic device (520) in the FIG. 5example) that may capture video image(s) to be coded by the videoencoder (503). In another example, the video source (501) is a part ofthe electronic device (520).

The video source (501) may provide the source video sequence to be codedby the video encoder (503) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (501) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (501) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (503) may code andcompress the pictures of the source video sequence into a coded videosequence (543) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (550). In some embodiments, the controller(550) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (550) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (550) can be configured to have other suitablefunctions that pertain to the video encoder (503) optimized for acertain system design.

In some embodiments, the video encoder (503) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (530) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (533)embedded in the video encoder (503). The decoder (533) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bit stream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (534). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (534) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder, such as the video decoder (410), which has alreadybeen described in detail above in conjunction with FIG. 4. Brieflyreferring also to FIG. 4, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (545) and the parser (420) can be lossless, the entropy decodingparts of the video decoder (410), including the buffer memory (415), andparser (420) may not be fully implemented in the local decoder (533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (530) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (532) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (534). In this manner, the video encoder(503) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new picture to be coded, the predictor(535) may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the source coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder (545)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (503) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the video encoder (503).During coding, the controller (550) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (503) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The source coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 6 shows a diagram of a video encoder (603) according to anotherembodiment of the disclosure. The video encoder (603) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (603) is used in theplace of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (603) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (603) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(603) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (603) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the interencoder (630), an intra encoder (622), a residue calculator (623), aswitch (626), a residue encoder (624), a general controller (621), andan entropy encoder (625) coupled together as shown in FIG. 6.

The inter encoder (630) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (622) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (622) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (621) is configured to determine general controldata and control other components of the video encoder (603) based onthe general control data. In an example, the general controller (621)determines the mode of the block, and provides a control signal to theswitch (626) based on the mode. For example, when the mode is the intramode, the general controller (621) controls the switch (626) to selectthe intra mode result for use by the residue calculator (623), andcontrols the entropy encoder (625) to select the intra predictioninformation and include the intra prediction information in the bitstream; and when the mode is the inter mode, the general controller(621) controls the switch (626) to select the inter prediction resultfor use by the residue calculator (623), and controls the entropyencoder (625) to select the inter prediction information and include theinter prediction information in the bit stream.

The residue calculator (623) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (622) or the inter encoder (630). Theresidue encoder (624) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (624) is configured to convert the residuedata in the frequency domain, and generate the transform coefficients.The transform coefficients are then subject to quantization processingto obtain quantized transform coefficients. In various embodiments, thevideo encoder (603) also includes a residue decoder (628). The residuedecoder (628) is configured to perform inverse-transform, and generatethe decoded residue data. The decoded residue data can be suitably usedby the intra encoder (622) and the inter encoder (630). For example, theinter encoder (630) can generate decoded blocks based on the decodedresidue data and inter prediction information, and the intra encoder(622) can generate decoded blocks based on the decoded residue data andthe intra prediction information. The decoded blocks are suitablyprocessed to generate decoded pictures and the decoded pictures can bebuffered in a memory circuit (not shown) and used as reference picturesin some examples.

The entropy encoder (625) is configured to format the bit stream toinclude the encoded block. The entropy encoder (625) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (625) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bit stream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 7 shows a diagram of a video decoder (710) according to anotherembodiment of the disclosure. The video decoder (710) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (710) is used in the place of the videodecoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropydecoder (771), an inter decoder (780), a residue decoder (773), areconstruction module (774), and an intra decoder (772) coupled togetheras shown in FIG. 7.

The entropy decoder (771) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (772) or the inter decoder (780), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (780); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (772). The residual information can be subject to inversequantization and is provided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (772) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (773) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (773) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (771) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (774) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (773) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (303), (503), and (603), and thevideo decoders (310), (410), and (710) can be implemented using anysuitable technique. In an embodiment, the video encoders (303), (503),and (603), and the video decoders (310), (410), and (710) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (303), (503), and (503), and the videodecoders (310), (410), and (710) can be implemented using one or moreprocessors that execute software instructions.

Aspects of the disclosure provide techniques to simplify affine motioncompensation with prediction offsets.

Generally, a motion vector for a block can be coded either in anexplicit way, to signal the difference to a motion vector predictor(e.g., advanced motion vector prediction or AMVP mode); or in animplicit way, to be indicated completely from one previously coded orgenerated motion vector. The later one is referred to as merge mode,meaning the current block is merged into a previously coded block byusing its motion information.

Both the AMVP mode and the merge mode construct candidate list duringdecoding.

II. Inter Prediction Coding Techniques

1. Merge Mode

In various embodiments, a picture can be partitioned into blocks, forexample, using a tree structure based partition scheme. The resultingblocks can then be processed with different processing modes, such as anintra prediction mode, an inter prediction mode (e.g., merge mode, skipmode, advanced motion vector prediction (AVMP mode), and the like. Whena currently processed block, referred to as a current block, isprocessed with a merge mode, a neighboring block can be selected from aspatial or temporal neighborhood of the current block. The current blockcan be merged with the selected neighboring block by sharing a same setof motion data (or referred to as motion information) from the selectedneighboring block. This merge mode operation can be performed over agroup of neighboring blocks, such that a region of neighboring blockscan be merged together and share a same set of motion data. Duringtransmission from an encoder to a decoder, an index indicating themotion data of the selected neighboring block can be transmitted for thecurrent block, instead of transmission of the whole set of motion data.In this way, an amount of data (bits) that are used for transmission ofmotion information can be reduced, and coding efficiency can beimproved.

In the above example, the neighboring block, which provides the motiondata, can be selected from a set of candidate positions. The candidatepositions can be predefined with respect to the current block. Forexample, the candidate positions can include spatial candidate positionsand temporal candidate positions. Each spatial candidate position isassociated with a spatial neighboring block neighboring the currentblock. Each temporal candidate position is associated with a temporalneighboring block located in another coded picture (e.g., a previouslycoded picture). Neighboring blocks overlapping the candidate positions(referred to as candidate blocks) are a subset of all the spatial ortemporal neighboring blocks of the current block. In this way, thecandidate blocks can be evaluated for selection of a to-be-merged blockinstead of the whole set of neighboring blocks.

FIG. 8 shows an example of candidate positions. From those candidatepositions, a set of merge candidates can be selected to construct amerge candidate list. As shown, a current block (810) is to be processedwith merge mode. A set of candidate positions {A1, B1, B0, A0, B2, C0,C1} are defined for the merge mode processing. Specifically, candidatepositions {A1, B1, B0, A0, B2} are spatial candidate positions thatrepresent positions of candidate blocks that are in the same picture asthe current block (810). In contrast, candidate positions {C0, C1} aretemporal candidate positions that represent positions of candidateblocks that are in another coded picture and neighbor or overlap aco-located block of the current block (810). As shown, the candidateposition C1 can be located near (e.g., adjacent to) a center of thecurrent block (810).

A candidate position can be represented by a block of samples or asample in different examples. In FIG. 8, each candidate position isrepresented by a block of samples, for example, having a size of 4×4samples. A size of such a block of samples corresponding to a candidateposition can be equal to or smaller than a minimum allowable size of PBs(e.g., 4×4 samples) defined for a tree-based partitioning scheme usedfor generating the current block (810). Under such a configuration, ablock corresponding to a candidate position can always be covered withina single neighboring PB. In an alternative example, a sample position(e.g., a bottom-right sample within the block A1, or a top-right samplewithin the block A0) may be used to represent a candidate position. Sucha sample is referred to as a representative sample, while such aposition is referred to as a representative position.

In one example, based on the candidate positions {A1, B1, B0, A0, B2,C0, C1} defined in FIG. 8, a merge mode process can be performed toselect merge candidates from the candidate positions {A1, B1, B0, A0,B2, C0, C1} to construct a candidate list. The candidate list can have apredefined maximum number of merge candidates, represented as Cm. Eachmerge candidate in the candidate list can include a set of motion datathat can be used for motion-compensated prediction.

The merge candidates can be listed in the candidate list according to acertain order. For example, depending on how the merge candidate isderived, different merge candidates may have different probabilities ofbeing selected. The merge candidates having higher probabilities ofbeing selected are positioned in front of the merge candidates havinglower probabilities of being selected. Based on such an order, eachmerge candidate is associated with an index (referred to as a mergeindex). In one embodiment, a merge candidate having a higher probabilityof being selected will have a smaller index value such that fewer bitsare needed for coding the respective index.

In one example, the motion data of a merge candidate can includehorizontal and vertical motion vector displacement values of one or twomotion vectors, one or two reference picture indices associated with theone or two motion vectors, and optionally an identification of whichreference picture list is associated with an reference picture index.

In an example, according to a predefined order, a first number of mergecandidates, Ca, is derived from the spatial candidate positionsaccording to the order {A1, B1, B0, A0, B2}, and a second number ofmerge candidates, Cb=Cm−Ca, is derived from the temporal candidatepositions according to the order {C0, C1}. The numerals A1, B1, B0, A0,B2, C0, C1 for representing candidate positions can also be used torefer to merge candidates. For example, a merge candidate obtained fromcandidate position A1 is referred to as the merge candidate A1.

In some scenarios, a merge candidate at a candidate position may beunavailable. For example, a candidate block at a candidate position canbe intra-predicted, outside of a slice or tile including the currentblock (810), or not in a same coding tree block (CTB) row as the currentblock (810). In some scenarios, a merge candidate at a candidateposition may be redundant. For example, one neighboring block of thecurrent block (810) can overlap two candidate positions. The redundantmerge candidate can be removed from the candidate list (e.g., byperforming a pruning process). When a total number of available mergecandidates (with redundant candidates being removed) in the candidatelist is smaller than the maximum number of merge candidates Cm,additional merge candidates can be generated (e.g., according to apreconfigured rule) to fill the candidate list such that the candidatelist can be maintained to have a fixed length. For example, additionalmerge candidates can include combined bi-predictive candidates and zeromotion vector candidates.

After the candidate list is constructed, at an encoder, an evaluationprocess can be performed to select a merge candidate from the candidatelist. For example, rate-distortion (RD) performance corresponding toeach merge candidate can be calculated, and the one with the best RDperformance can be selected. Accordingly, a merge index associated withthe selected merge candidate can be determined for the current block(810) and signaled to a decoder.

At a decoder, the merge index of the current block (810) can bereceived. A similar candidate list construction process, as describedabove, can be performed to generate a candidate list that is the same asthe candidate list generated at the encoder side. After the candidatelist is constructed, a merge candidate can be selected from thecandidate list based on the received merge index without performing anyfurther evaluations in some examples. Motion data of the selected mergecandidate can be used for a subsequent motion-compensated prediction ofthe current block (810).

A skip mode is also introduced in some examples. For example, in theskip mode, a current block can be predicted using a merge mode asdescribed above to determine a set of motion data, however, no residueis generated, and no transform coefficients are transmitted. A skip flagcan be associated with the current block. The skip flag and a mergeindex indicating the related motion information of the current block canbe signaled to a video decoder. For example, at the beginning of a CU inan inter-picture prediction slice, a skip flag can be signaled thatimplies the following: the CU only contains one PU (2N×2N); the mergemode is used to derive the motion data; and no residual data is presentin the bitstream. At the decoder side, based on the skip flag, aprediction block can be determined based on the merge index for decodinga respective current block without adding residue information. Thus,various methods for video coding with merge mode disclosed herein can beutilized in combination with a skip mode.

As an example, in an embodiment, when a merge flag or a skip flag issignaled as true in a bit stream, a merge index is then signaled toindicate which candidate in a merge candidate list will be used toprovide motion vectors for a current block. Up to four spatiallyneighboring motion vectors and up to one temporally neighboring motionvectors can be added to the merge candidate list. A syntaxMaxMergeCandsNum is defined as the size of the merge candidate list. Thesyntax MaxMergeVandsNum can be signaled in the bit stream.

2. Extended Merge Prediction Mode

In some embodiments, the above described merge candidate list isexpanded, and an extended merge candidate list is used in merge mode.For example, the extended merge candidate list can be constructed byincluding the following five types of merge candidates sequentiallysubject to a maximum allowed size of merge candidates on the list:

-   -   1) Spatial motion vector predictor (MVP) from spatial neighbor        coding units (CUs);    -   2) Temporal MVP from collocated CUs;    -   3) History-based MVP from a history buffer;    -   4) Pairwise average MVP; and    -   5) Zero MVs.        The term, coding unit, can refer to a prediction block, or a        coding block partitioned from a picture.

In various embodiments, a size of the extended merge list can besignaled in a slice header, a tile group header, and the like. In anexample, a maximum allowed size of an extended merge list is 6. In someembodiments, for a CU coded in merge mode, an index of a best mergecandidate is encoded using truncated unary binarization (TU). The firstbin of the merge index can be coded with context, and other bins can becoded with bypass coding.

Generation processes of different types of merge candidates on theextended merge candidate list are described below.

2.1 Spatial Candidates Derivation

In an embodiment, the derivation of spatial merge candidates in anextended merge list is similar to that of the spatial merge candidatesas described in section II. 1 Merge Mode. FIG. 9 shows spatial mergecandidate positions of a current block (910) in accordance with anembodiment. A maximum of four merge candidates can be selected andderived among the candidate positions shown in FIG. 9. The order of thederivation can be A1, B1, B0, A0 and B2 in one example. In an example,the position B2 is considered only when any CU of position A1, B1, B0,A0 is not available (e.g., because it belongs to another slice or tile)or is intra coded.

After a candidate at position A1 is added to the extended candidatelist, the addition of the other candidates can be subject to aredundancy check. By the redundancy check, merge candidates with samemotion information are excluded from the extended merge list so that acoding efficiency can be improved. To reduce computational complexity,in an example, not all possible candidate pairs are considered in theredundancy check. Instead, only pairs linked with an arrow in FIG. 10are considered. A candidate is not added to the merge list if acounterpart indicated in FIG. 10 is in the merge list and has the sameor similar motion information as the to-be-added candidate in someexamples.

2. 2 Temporal Candidates Derivation

In an embodiment, only one temporal candidate is added to the extendedmerge list. FIG. 11 shows an example of deriving a temporal mergecandidate (1131) of a current block (1111) in a current picture (1101)in accordance with an embodiment. The temporal merge candidate (1131) isderived by scaling a motion vector (1132) of a co-located block (1112)of the current block (1111) in a picture (1102) (referred to as aco-located picture). In an example, a reference picture index of theco-located picture is explicitly signaled, for example, in a sliceheader. In an example, a reference picture index of the temporal mergecandidate (1131) is set to 0. In an embodiment, the scaling operation isbased on distances of picture order count (POC), Tb (1141) and Td(1142). For example, Tb (1141) is defined to be a POC distance between areference picture (1103) of the current block (1111) and the currentpicture (1101), while Td (1142) is defined to be a POC distance betweena reference picture (1104) of the co-located block (1112) and theco-located picture (1102).

FIG. 12 shows candidate positions, C1 and C0, from which a temporalmerge candidate of current block 1210 can be selected in accordance withan embodiment. In an embodiment, the position C0 is first checked toderive the temporal merge candidate. If a merge candidate at theposition C0 is not available, for example, when a neighbor block at theC0 is not available, intra coded, or is outside of the current row ofCTUs, the position C1 is used.

2.3 History-Based Merge Candidates Derivation

In some embodiments, history-based motion vector prediction (HMVP) mergecandidates are added to an extended merge list of a current CU after thespatial and temporal candidate motion vector predictor (MVP). In HMVP,motion information of a previously coded block can be stored in a table(or a history buffer) and used as a MVP candidate for the current CU.Such motion information is referred to as HMVP candidates. The tablewith multiple HMVP candidates can be maintained during an encoding ordecoding process. The table can be reset (emptied) when a new CTU row isencountered in one example. Whenever there is a non-subblock inter-codedCU, the associated motion information can be added to a last entry ofthe table as a new HMVP candidate in an embodiment.

In an embodiment, a size of an HMVP table, denoted by S, is set to be 6.Accordingly, up to 6 HMVP candidates may be added to the table. Wheninserting a new motion candidate to the table, a constrainedfirst-in-first-out (FIFO) rule can be utilized in an embodiment. Inaddition, a redundancy check can be applied when adding a new HMVPcandidate to find whether there is an identical HMVP in the table. Iffound, the identical HMVP candidate is removed from the table and allthe HMVP candidates following the removed HMVP candidate are movedforward. The new HMVP candidate can then be added at the end of thetable.

In an embodiment, HMVP candidates are used in an extended mergecandidate list construction process. The latest several HMVP candidatesin the table can be checked in order and inserted to the extendedcandidate list at positions after TMVP candidate in an embodiment. Aredundancy check may be applied to determine if the HMVP candidates issimilar or the same as a spatial or temporal merge candidate previouslyadded to the extended merge list.

To reduce the number of redundancy check operations, the followingsimplifications are introduced in an embodiment:

(i) Number of HMPV candidates used for generation of an extended mergelist is set as N<=4 and M=(8−N), wherein N indicates a number ofexisting candidates in the extended merge list and M indicates a numberof available HMVP candidates in a history table.

(ii) Once a total number of available merge candidates in the extendedmerge list reaches a number of the maximally allowed merge candidatesminus 1, the merge candidate list construction process from HMVP isterminated.

2.4 Pair-Wise Average Merge Candidates Derivation

In some embodiments, pairwise average candidates can be generated byaveraging predefined pairs of candidates in a current merge candidatelist. For example, the predefined pairs are defined as {(0, 1), (0, 2),(1, 2), (0, 3), (1, 3), (2, 3)} in an embodiment, where the numbersdenote the merge indices to the merge candidate list. For example, theaveraged motion vectors are calculated separately for each referencepicture list. If both to-be-averaged motion vectors are available in onelist, these two motion vectors are averaged even when they point todifferent reference pictures. If only one motion vector is available,the available one can be used directly. If no motion vector isavailable, the respective pair is skipped in one example.

2.5 Zero Motion Vector Predictors

In some embodiments, when an extended merge list is not full afterpair-wise average merge candidates are added, zero MVPs are inserted atthe end of the extended merge list until a maximum allowed mergecandidate number is reached.

3. Triangular Prediction Mode (TPM)

A triangular prediction mode (TPM) can be employed for inter predictionin some embodiments. In an embodiment, the TPM is applied to CUs thatare 8×8 samples or larger in size and are coded in skip or merge mode.In an embodiment, for a CU satisfying these conditions (8×8 samples orlarger in size and coded in skip or merge mode), a CU-level flag issignaled to indicate whether the TPM is applied or not.

When the TPM is used, in some embodiments, a CU is split evenly into twotriangle-shaped partitions, using either the diagonal split or theanti-diagonal split as shown in FIG. 13. In FIG. 13, a first CU (1310)is split from a top-left corner to a bottom-right corner resulting intwo triangular prediction units, PU1 and PU2. A second CU (1320) issplit from a top-right corner to a bottom-left corner resulting in twotriangular prediction units, PU1 and PU2. Each triangular predictionunit PU1 or PU2 in the CU (1310) or CU (1320) is inter-predicted usingits own motion information. In some embodiments, only uni-prediction isallowed for each triangular prediction unit. Accordingly, eachtriangular prediction unit has one motion vector and one referencepicture index. The uni-prediction motion constraint can be applied toensure that, similar to a conventional bi-prediction method, not morethan two motion compensated predictions are performed for each CU. Inthis way, processing complexity can be reduced. The uni-predictionmotion information for each triangular prediction unit can be derivedfrom a uni-prediction merge candidate list. In some other embodiments,bi-prediction is allowed for each triangular prediction unit.Accordingly, the bi-prediction motion information for each triangularprediction unit can be derived from a bi-prediction merge candidatelist.

In some embodiments, when a CU-level flag indicates that a current CU iscoded using the TPM, an index, referred to as triangle partition index,is further signaled. For example, the triangle partition index can havea value in a range of [0, 39]. Using this triangle partition index, thedirection of the triangle partition (diagonal or anti-diagonal), as wellas the motion information for each of the partitions (e.g., mergeindices (or referred to as TPM indices) to the respective uni-predictioncandidate list) can be obtained through a lookup table at the decoderside. After predicting each of the triangular prediction unit based onthe obtained motion information, in an embodiment, the sample valuesalong the diagonal or anti-diagonal edge of the current CU are adjustedby performing a blending process with adaptive weights. As a result ofthe blending process, a prediction signal for the whole CU can beobtained. Subsequently, a transform and quantization process can beapplied to the whole CU in a way similar to other prediction modes.Finally, a motion field of a CU predicted using the triangle partitionmode can be created, for example, by storing motion information in a setof 4×4 units partitioned from the CU. The motion field can be used, forexample, in a subsequent motion vector prediction process to construct amerge candidate list.

3.1 Uni-Prediction Candidate List Construction

In some embodiments, a merge candidate list for prediction of twotriangular prediction units of a coding block processed with a TPM canbe constructed based on a set of spatial and temporal neighboring blocksof the coding block. Such a merge candidate list can be referred to as aTPM candidate list or triangle merger mode candidate list with TPMcandidates listed herein. In one embodiment, the merge candidate list isa uni-prediction candidate list. The uni-prediction candidate listincludes five uni-prediction motion vector candidates in an embodiment.For example, the five uni-prediction motion vector candidates arederived from seven neighboring blocks including five spatial neighboringblocks (labeled with numbers of 1 to 5 in FIG. 14) and two temporalco-located blocks (labeled with numbers of 6 to 7 in FIG. 14).

In an example, the motion vectors of the seven neighboring blocks arecollected and included in the uni-prediction candidate list according tothe following order: first, the motion vectors of the uni-predictedneighboring blocks; then, for the bi-predicted neighboring blocks, theL0 motion vectors (that is, the L0 motion vector part of thebi-prediction MV), the L1 motion vectors (that is, the L1 motion vectorpart of the bi-prediction MV), and averaged motion vectors of the L0 andL1 motion vectors of the bi-prediction MVs. In an embodiment, if thenumber of candidates is less than five, zero motion vectors are added tothe end of the list. In some other embodiments, the merge candidate listmay include less than 5 or more than 5 uni-prediction or bi-predictionmerge candidates that are selected from candidate positions that are thesame or different from that shown in FIG. 14.

3.2 Lookup Table and Table Indices

In an embodiment, a CU is coded with a triangular partition mode with aTPM (or merge) candidate list including five TPM candidates.Accordingly, there are 40 possible ways to predict the CU when 5 mergecandidates are used for each triangular PU. In other words, there can be40 different combinations of split directions and merge (or TPM)indices: 2 (possible split directions)×(5 (possible merge indices for afirst triangular prediction unit)×5 (possible merge indices for a secondtriangular prediction unit)−5 (a number of possibilities when the pairof first and second prediction units shares a same merge index)). Forexample, when a same merge index is determined for the two triangularprediction units, the CU can be processed using a regular merge mode,instead of the triangular predication mode.

Accordingly, in an embodiment, a triangular partition index in the rangeof [0, 39] can be used to represent which one of the 40 combinations isused based on a lookup table. FIG. 15 shows an exemplary lookup table(1500) used to derive the split direction and merge indices based on atriangular partition index. As shown in the lookup table (1500), a firstrow (1501) includes the triangular partition indices ranging from 0 to39; a second row (1502) includes possible split directions representedby 0 or 1; a third row (1503) includes possible first merge indicescorresponding to a first triangular prediction unit and ranging from 0to 4; and, a fourth row 1504 includes possible second merge indicescorresponding to a second triangular prediction unit and ranging from 0to 4.

For example, when a triangular partition index having a value of 1 isreceived at a decoder, based on a column (1520) of the lookup table(1500), it can be determined that the split direction is a partitiondirection represented by the value of 1, and the first and second mergeindices are 0 and 1, respectively. As the triangle partition indices areassociated with a lookup table, a triangle partition index is alsoreferred to as a table index in this disclosure.

3.3 Adaptive Blending along the Triangular Partition Edge

In an embodiment, after predicting each triangular prediction unit usingrespective motion information, a blending process is applied to the twoprediction signals of the two triangular prediction units to derivesamples around the diagonal or anti-diagonal edge. The blending processadaptively chooses between two groups of weighting factors depending onthe motion vector difference between the two triangular predictionunits. In an embodiment, the two weighting factor groups are as follows:

(1) 1st weighting factor group: {7/8, 6/8, 4/8, 2/8, 1/8} for samples ofa luma component and {7/8, 4/8, 1/8} for samples of chroma component;and

(2) 2nd weighting factor group: {7/8, 6/8, 5/8, 4/8, 3/8, 2/8, 1/8} forsamples of a luma component and {6/8, 4/8, 2/8} for samples of a chromacomponent. The second weighting factor group has more luma weightingfactors and blends more luma samples along the partition edge.

In an embodiment, the following condition is used to select one of thetwo weighting factor groups. When reference pictures of the two trianglepartitions are different from each other, or when a motion vectordifference between the two triangle partitions is larger than athreshold (e.g., 16 luma samples), the 2nd weighting factor group isselected. Otherwise, the 1st weighting factor group is selected.

FIG. 16 shows an example of a CU applying the first weighting factorgroup. As shown, a first coding block (1601) includes luma samples, anda second coding block (1602) includes chroma samples. A set of pixelsalong a diagonal edge in the coding block (1601) or (1602) are labeledwith the numbers 1, 2, 4, 6, and 7 corresponding to the weightingfactors 7/8, 6/8, 4/8, 2/8, and 1/8, respectively. For example, for apixel labelled with the number of 2, a sample value of the pixel after ablending operation can be obtained according to:

the blended sample value=2/8×P1+6/8×P2,

where P1 and P2 represent sample values at the respective pixel butbelong to predictions of a first triangular prediction unit and a secondtriangular prediction unit, respectively.

FIG. 17 shows an example of a CU applying the second weighting factorgroup. As shown, a first coding block (1701) includes luma samples, anda second coding block (1702) includes chroma samples. A set of pixelsalong a diagonal edge in the coding block (1701) or (1702) are labeledwith the numbers 1, 2, 3, 4, 5, 6, and 7 corresponding to the weightingfactors 7/8, 6/8, 5/8, 4/8, 3/8, 2/8, 1/8, respectively. For example,for a pixel labeled with the number of 3, a sample value of the pixelafter a blending operation can be obtained according to:

the blended sample value=3/8×P1+5/8×P2,

where P1 and P2 represent sample values at the respective pixel butbelong to predictions of a first triangular prediction unit and a secondtriangular prediction unit, respectively.

3.4 Syntax Elements for Signaling Triangular Prediction Parameters

In some embodiments, a triangular prediction unit mode is applied to CUsin skip or merge mode. A block size of the CUs cannot be smaller than8×8. For a CU coded in a skip or merge mode, a CU level flag is signaledto indicate whether the triangular prediction unit mode is applied ornot for the current CU. In an embodiment, when the triangular predictionunit mode is applied to the CU, a table index indicating the directionfor splitting the CU into two triangular prediction units and the motionvectors (or respective merge indices) of the two triangular predictionunits are signaled. The table index ranges from 0 to 39. A lookup table,such as the table described in FIG. 15, is used for deriving thesplitting direction and motion vectors from the table index.

As descried above, three parameters, a split direction, a first mergeindex (TPM index) corresponding to a first triangular prediction unit,and a second merge index (TPM index) corresponding to a secondtriangular prediction unit, are generated when a TPM is applied to acoding block. As described, in some examples, the three triangularprediction parameters are signaled from an encoder side to a decoderside by signaling a table index. Based on a lookup table (e.g., thelookup table (1500) in the FIG. 15 example), the three triangularprediction parameters can be derived using the table index received atthe decoder side. However, additional memory space is required forstoring the lookup table at a decoder, which may become a burden in someimplementations of the decoder. For example, the additional memory maylead to an increase in cost and power consumption of the decoder.

To solve the above problem, in some embodiments, instead of signaling atable index and relying on a lookup table to interpret the table index,three syntax elements are signaled from an encoder side to a decoderside. The three triangular prediction parameters (the split directionand two merge or TPM indices) can be derived or determined at thedecoder side based on the three syntax elements without using the lookuptable. The three syntax elements can be signaled in any order for therespective coding block in an embodiment.

In an embodiment, the three syntax elements include a split directionsyntax element, a first index syntax element, and a second index syntaxelement. The split direction syntax element can be used to determine thesplit direction parameter. The first and second index syntax elements incombination can be used to determine the parameters of the first andsecond merge or TPM indices.

For the split direction syntax element, in an embodiment, the splitdirection syntax element takes a value of 0 or 1 to indicate whether thesplit direction is from a top-left corner to a bottom-right corner orfrom a top-right corner to a bottom-left corner.

For the first and second index syntax elements, in an embodiment, thefirst index syntax element is configured to have a value of theparameter of the first merge index, while the second index syntaxelement is configured to have a value of the second merge index when thesecond merge index is smaller than the first merge index, and have avalue of the second merge index minus one when the second merge index isgreater than the first merge index (the second and first merge index aresupposed to take different value as described above, so the second andfirst merge index are not the same).

As an example, in an embodiment, a merge candidate list has a length of5 merge candidates. Accordingly, the first index syntax element takes avalue of 0, 1, 2, 3, or 4, while the second index syntax element takes avalue of 0, 1, 2, or 3. For example, in a case that the first mergeindex parameter has a value of 2, and the second merge index parameterhas a value of 4, to signal the first and second merge index, the firstand second index syntax elements would have a value of 2 and 3,respectively.

In an embodiment, a coding block is located at a position havingcoordinates of (xCb, yCb) with respect to a reference point in a currentpicture, where xCb and yCb represent the horizontal and verticalcoordinates of the current coding block, respectively. In someembodiments, xCb and yCb are aligned with the horizontal and verticalcoordinates with 4×4 granularity. Accordingly, the split directionsyntax element is represented as split_dir[xCb][yCb]. The first indexsyntax element is represented as merge_triangle_idx0[xCb][yCb] and thesecond index syntax element is represented asmerge_triangle_idx1[xCb][yCb].

For example, in VVC working draft 4 (JVET-M1001), the syntax of themerge mode and the TPM, and related semantics are as described in Table1.

TABLE 1 Descriptor merge_data( x0, y0, cbWidth, cbHeight ) { if (CuPredMode[ x0 ][ y0 ] = = MODE_IBC ) { if( MaxNumMergeCand > 1 )merge_idx[ x0 ][ y0 ] ae(v) } else { mmvd_flag[ x0 ][ y0 ] ae(v) if(mmvd_flag[ x0 ][ y0] = = 1 ) { mmvd_merge_flag[ x0 ][ y0 ] ae(v)mmvd_distance_idx[ x0 ][ y0 ] ae(v) mmvd_direction_idx[ x0 ][ y0 ] ae(v)} else { if( MaxNumSubblockMergeCand > 0 && cbWidth >= 8 && cbHeight >=8 ) merge_subblock_flag[ x0 ][ y0 ] ae(v) if( merge_subblock_flag[ x0 ][y0 ] = = 1 ) { if( MaxNumSubblockMergeCand > 1 ) merge_subblock_idx[ x0][ y0 ] ae(v) } else { if( sps_ciip_enabled_flag && cu_skip_flag[ x0 ][y0 ] = = 0 && ( cbWidth * cbHeight) >= 64 && cbWidth < 128 && cbHeight <128 ) { ciip_flag[ x0 ][ y0 ] ae(v) if( ciip_flag[ x0 ][ y0 ] ) { if (cbWidth <= 2 * cbHeight | | cbHeight <= 2 * cbWidth )ciip_luma_mpm_flag[ x0 ][ y0 ] ae(v) if( ciip_luma_mpm_flag[ x0 ][ y0 ]) ciip_luma_mpm_idx[ x0 ][ y0 ] ae(v) } } if( sps_triangle_enabled_flag&& tile_group_type = = B && ciip_flag[ x0 ][ y0 ] = = 0 && cbWidth *cbHeight >= 64 ) merge_triangle_flag[ x0 ][ y0 ] ae(v) if(merge_triangle_flag[ x0 ][ y0 ] ) { merge_triangle_split_dir[ x0 ][ y0 ]ae(v) merge_triangle_idx0[ x0 ][ y0 ] ae(v) merge_triangle_idx1[ x0 ][y0 ] ae(v) } else if( MaxNumMergeCand > 1 ) merge_idx[ x0 ][ y0 ] ae(v)} } } }

In Table 1, if merge_triangle_flag[x0][y0] equals to 1, it specifiesthat for the current coding unit, when decoding a tile group, triangularshape based motion compensation is used to generate the predictionsamples of the current coding unit. If merge_triangle_flag[x0][y0]equals to 0, it specifies that the coding unit is not predicted bytriangular shape based motion compensation. Whenmerge_triangle_flag[x0][y0] is not present, it is inferred to be equalto 0. In addition, merge_triangle_split_dir[x0][y0] specifies thesplitting direction of merge triangle mode. The array indices x0, y0specify the location (x0, y0) of the top-left luma sample of the codingblock relative to the top-left luma sample of the picture. Whenmerge_triangle_split_dir[x0][y0] is not present, it is inferred to beequal to 0. Further, merge_triangle_idx0[x0][y0] specifies the firstmerging candidate index of the triangular shape based motioncompensation candidate list where x0, y0 specify the location (x0, y0)of the top-left luma sample of the coding block relative to the top-leftluma sample of the picture. When merge_triangle_idx0[x0][y0] is notpresent, it is inferred to be equal to 0. Similarly,merge_triangle_idx1[x0][y0] specifies the second merging candidate indexof the triangular shape based motion compensation candidate list wherex0, y0 specify the location (x0, y0) of the top-left luma sample of thecoding block relative to the top-left luma sample of the picture. Whenmerge_triangle_idx1[x0][y0] is not present, it is inferred to be equalto 0.

III. Flexible Maximum Allowed Number of TPM Candidates

As described above, in some examples, a TPM candidate list may include afixed number of 5 TMP candidates. However, under certain situations, themaximum allowed number of TMP candidates is desired to be flexible inorder to achieve a better tradeoff between complexity and codingefficiency. Accordingly, in some embodiments, a maximum allowed numberof TPM candidates for coding a set of blocks with TPM can be signaled ina bit stream. For example, the maximum allowed number of TPM candidatescan be signaled in a sequence parameter set (SPS), a picture parameterset (PPS), a slice header, a tile header, a tile group header, or thelike. In some embodiments, the maximum allowed number of TMP candidatesis denoted by MaxNumTriangleMergeCand.

In an embodiment, a maximum allowed number of TPM candidates isrestricted to be an integer from 0 to a maximum allowed number of mergecandidates in a merge mode. The merge mode can be the merge modedescribed at the section of II.1 or the extended merge prediction modedescribed at the section of II.2. For example, in an embodiment, themerge mode that provides a basis for limiting the maximum allowed numberof TPM candidates can include the following types of merge candidates:(i) Spatial motion vector predictor (MVP) from spatial neighbor codingunits (CUs); (ii) Temporal MVP from collocated CUs; (iii) History-basedMVP from a history buffer; or (iv) Pairwise average MVP, and may notinclude affine based merge candidates or sub-block based mergecandidates.

In various examples, the maximum allowed number of merge mode candidatescan be different. In an embodiment, the maximum allowed number of mergemode candidates can be 5 or 6. In an embodiment, limiting the maximumallowed number of TPM candidates by the maximum allowed number of mergemode candidates can reduce implementation complexity of an encoder ordecoder that employs both TPM and merge mode as coding tool options.

In an embodiment, a maximum allowed number of TPM candidates is signaleddirectly. For example, a syntax element having a value equal to themaximum allowed number of TPM candidates can be signaled.

In an embodiment, to improve coding efficiency, a difference between amaximum allowed number of TPM candidates and a maximum allowed number ofmerge mode candidates is signaled. The maximum allowed number of mergemode candidates may be signaled in a tile group header. In anembodiment, a maximum allowed number of merge mode candidates issignaled first. Then, a difference between the maximum allowed number ofmerge mode candidates and a maximum allowed number of TPM candidates issignaled. The maximum allowed number of TPM candidates is only signaledwhen the maximum allowed number of merge mode candidates is not smallerthan 2. In another embodiment, if the maximum allowed number of mergemode candidates is not signaled, the maximum allowed number of TPMcandidates is inferred as 0. In another embodiment, the maximum allowednumber of TPM candidates is not allowed to be greater than the maximumallowed number of merge mode candidates. In another embodiment, themaximum allowed number of TPM candidates is not signaled, but set to themaximum allowed number of merge mode candidates.

In an embodiment, max_num_merge_cand_minus_max_num_triangle_cand issignaled, which specifies the maximum allowed number of TPM candidatessupported in the tile group subtracted from the maximum allowed numberof merge mode candidates, denoted as MaxNumMergeCand. Thus, the maximumallowed number of TPM candidates, MaxNumTriangleMergeCand can bedetermined according to:

MaxNumTriangleMergeCand=MaxNumMergeCand−max_num_merge_cand_minus_max_num_triangle_cand

In an embodiment, the value of MaxNumTriangleMergeCand can either equalsto 0, or is an integer from 2 to the maximum allowed number of mergecandidates. In an embodiment, whenmax_num_merge_cand_minus_max_num_triangle_cand is not signaled,MaxNumTriangleMergeCand is infered as 0. In an embodiment, whenMaxNumTriangleMergeCand is 0, TPM is not allowed to be used for the tilegroup.

Table 2 shows an example of syntax transmission according to the aboveembodiment. In Table 2, tile_group_header( )) indicates a start of asyntax transmission of a tile group header. When thesps_triangle_enable_flag is true (indicating a TPM is enabled in an SPSthat regulates the current tile group) and the maximum allowed number ofmerge mode candidates is greater than or equal to 2, the syntax element,max_num_merge_cand_minus_max_num_triangle_cand is transmitted.

TABLE 2 Descriptor tile_group_header( ) {tile_group_pic_parameter_set_id ue(v) if( rect_tile_group_flag | |NumTilesInPic > 1 ) tile_group_address u(v) if( !rect_tile_group_flag &&!single_tile_per_tile_group_flag ) num_tiles_in_the_group_minus1 ue(v)tile_group_type ue(v) tile_group_pic_order_cnt_lsb u(v) if(nal_unit_type != IDR_W_RADL && nal_unit_type != IDR_N_LP ) { for( i = 0;i < 2; i++ ) { if( num_ref_pic_lists_in_sps[ i ] > 0 && ( i = = 0 | | (i = = 1 && rpl1_idx_present_flag ) ) ) ref_pic_list_sps_flag[ i ] u(1)if( ref_pic_list_sps_flag[ i ] ) { if( num_ref_pic_lists_in_sps[ i ] > 1&& ( i = = 0 | | ( i = = 1 && rpl1_idx_present_flag ) ) )ref_pic_list_idx[ i ] u(v) } else ref_pic_list_struct( i,num_ref_pic_lists_in_sps[ i ] ) for( j = 0; j < NumLtrpEntries[ i][RplsIdx[ i ] ]; j++ ) { delta_poc_msb_present_flag[ i ][ j ] u(1) if(delta_poc_msb_present_flag[ i ][ j ] ) delta_poc_msb_cycle_lt[ i ][ j ]ue(v) } } if( tile_group_type = = P | | tile_group_type = = B ) {num_ref_idx_active_override_flag u(1) if(num_ref_idx_active_override_flag ) for( i = 0; i < (tile_group_type = =B ? 2: 1 ); i++ ) if( num_ref_entries[ i ][ RplsIdx[ i ] ] > 1 )num_ref_idx_active_minus1[ i ] ue(v) } } if(partition_constraints_override_enabled_flag ) {partition_constraints_override_flag ue(v) if(partition_constraints_override_flag ) {tile_group_log2_diff_min_qt_min_cb_luma ue(v)tile_group_max_mtt_hierarchy_depth_luma ue(v) if(tile_group_max_mtt_hierarchy_depth_luma != 0 )tile_group_log2_diff_max_bt_min_qt_luma ue(v)tile_group_log2_diff_max_tt_min_qt_luma ue(v) } if( tile_group_type = =I && qtbtt_dual_tree_intra_flag ) {tile_group_log2_diff_min_qt_min_cb_chroma ue(v)tile_group_max_mtt_hierarchy_depth_chroma ue(v) if(tile_group_max_mtt_hierarchy_depth_chroma != 0 )tile_group_log2_diff_max_bt_min_qt_chroma ue(v)tile_group_log2_diff_max_tt_min_qt_chroma ue(v) } } } } if(tile_group_type != I ) { if( sps_temporal_mvp_enabled_flag )tile_group_temporal_mvp_enabled_flag u(1) if( tile_group_type = = B )mvd_l1_zero_flag u(1) if( cabac_init_present_flag ) cabac_init_flag u(1)if( tile_group_temporal_mvp_enabled_flag ) { if( tile_group_type = = B )collocated_from_l0_flag u(1) } if( ( weighted_pred_flag &&tile_group_type = = P ) | | ( weighted_bipred_flag && tile_group = = B )) pred_weight_table( ) six_minus_max_num_merge_cand ue(v) if(sps_affine_enabled_flag ) five_minus_max_num_subblock_merge_cand ue(v)if( sps_fpel_mmvd_enabled_flag ) tile_group_fpel_mmvd_enabled_flag u(1)if( sps_triangle_enabled_flag && MaxNumMergeCand >= 2 )max_num_merge_cand_minus_max_num_triangle_cand ue(v) } else if (sps_ibc_enabled_flag ) six_minus_max_num_merge_cand ue(v)tile_group_qp_delta se(v) if(pps_tile_group_chroma_qp_offsets_present_flag ) {tile_group_cb_qp_offset se(v) tile_group_cr_qp_offset se(v) } if(sps_sao_enabled_flag ) { tile_group_sao_luma_flag u(1) if(ChromaArrayType != 0 ) tile_group_sao_chroma_flag u(1) } if(sps_alf_enabled_flag ) { tile_group_alf_enabled_flag u(1) if(tile_group_alf_enabled_flag ) tile_group_aps_id u(5) }dep_quant_enabled_flag u(1) if( !dep_quant_enabled_flag )sign_data_hiding_enabled_flag u(1) if(deblocking_filter_override_enabled_flag )deblocking_filter_override_flag u(1) if( deblocking_filter_override_flag) { tile_group_deblocking_filter_disabled_flag u(1) if(!tile_group_deblocking_filter_disabled_flag ) {tile_group_beta_offset_div2 se(v) tile_group_tc_offset_div2 se(v) } }if( NumTilesInCurrTileGroup > 1 ) { offset_len_minus1 ue(v) for( i = 0;i < NumTilesInCurrTileGroup − 1; i++ ) entry_point_offset_minus1[ 1 ]u(v) } byte_alignment( ) }

In an embodiment, the usage of TPM may be limited based on the maximumallowed number of TPM candidates (denoted as MaxNumTriangleMergeCand)which is signaled in the tile group header. For example, TPM is onlyused when MaxNumTriangleMergeCand>=N. Otherwise, TPM should not be used.Table 3 shows an exemplary syntax table according to the aboveembodiment, where N=2. In Table 3, the merger triangle flag istransmitted only when the maximum number of triangular merge modecandidates is greater than or equal to 2. As a result, TPM is only usedwhen the maximum allowed number of TPM candidates is greater than orequal to 2.

TABLE 3 Descriptor  merge data( x0, y0, cbWidth, cbHeight ) { ...... if(sps_triangle_enabled_flag && tile_group_type = = B && ciip_flag[ x0 ][y0 ] = = 0 && cbWidth * cbHeight >= 64 && MaxNumTriangleMergeCand >= 2)merge_triangle_flag[ x0 ][ y0 ] ae(v) if( merge_triangle_flag[ x0 ][ y0] ) { merge_triangle_split_dir[ x0 ][ y0 ] ae(v) merge_triangle_idx0[ x0][ y0 ] ae(v) merge_triangle_idx1[ x0 ][ y0 ] ae(v) } else if(MaxNumMergeCand > 1 ) merge_idx[ x0 ][ y0 ] ae(v) } ...... }

In an embodiment, when MaxNumTriangleMergeCand is greater than 0, theindices of merge candidates to be used for the triangular merge mode(merge_triangle_idx0 and merge_triangle_idx1) may be signaled. The valueof merge_triangle_idx0 and merge_triangle_idx1 may be updated based onthe maximum allowed number of TPM candidates. For example, a maximumnumber of merge_triangle_idx0 equals to the maximum allowed number ofTPM candidates minus one, and a maximum number of merge_triangle_idx1equals to the maximum allowed number of TPM candidates minus two. Thebinarization of merge_triangle_idx0 and merge_triangle_idx1 is as shownin the following Table 4.

TABLE 4 merge_data( ) mmvd_flag[ ][ ] FL cMax = 1 mmvd_merge_flag[ ][ ]FL cMax = 1 mmvd_distance_idx[ ][ ] TR cMax = 7, cRiceParam = 0mmvd_direction_idx[ ][ ] FL cMax = 3 ciip_flag[ ][ ] FL cMax = 1clip_luma_mpm_flag[ ][ ] FL cMax = 1 clip_luma_mpm_idx[ ][ ] TR cMax =2, cRiceParam = 0 merge_subblock_flag[ ][ ] FL cMax = 1merge_subblock_idx[ ][ ] TR cMax = MaxNumSubblockMergeCand − 1,cRiceParam = 0 merge_triangle_flag[ ][ ] FL cMax = 1 merge_triangle_idx[][ ] FL cMax = 1 merge_triangle_idx0[ ][ ] TR cMax =MaxNumTriangleMergeCand − 1, cRiceParam = 0 merge_triangle_idx1[ ][ ] TRcMax = MaxNumTriangleMergeCand − 2, cRiceParam = 0 merge_idx[ ][ ] TRcMax = MaxNumMergeCand − 1, cRiceParam = 0

FIG. 18 shows a flow chart outlining a process (1800) according to anembodiment of the disclosure. The process (1800) can be used in thereconstruction of a block coded in intra mode, to generate a predictionblock for the block under reconstruction. The process (1800) can beexecuted by processing circuitry, such as the processing circuitry inthe terminal devices (210), (220), (230) and (240), the processingcircuitry that performs functions of the video encoder (303), theprocessing circuitry that performs functions of the video decoder (310),the processing circuitry that performs functions of the video decoder(410), the processing circuitry that performs functions of the intraprediction module (452), the processing circuitry that performsfunctions of the video encoder (503), the processing circuitry thatperforms functions of the predictor (535), the processing circuitry thatperforms functions of the intra encoder (622), the processing circuitrythat performs functions of the intra decoder (772), and the like. Insome embodiments, the process (1800) is implemented in softwareinstructions, thus when the processing circuitry executes the softwareinstructions, the processing circuitry performs the process (1800). Theprocess starts at (S1801) and proceeds to (S1810).

At (S1810), a first syntax element in a coded video bit stream isreceived. The first syntax element indicates a maximum allowed number ofmerge candidates in a set of coding blocks in the coded video bitstream. The syntax element can be signaled in an SPS, a PPS, a sliceheader, a tile header, a tile group header, or the like. Accordingly,the maximum allowed number of TPM candidates can be applied to a set ofcoding blocks controlled by the SPS, the PPS, the slice header, the tileheader, or the tile group header, respectively.

At (S1820), a maximum allowed number of triangular prediction mode (TPM)candidates for the set of coding blocks is set based on a second syntaxelement when the second syntax element is received, otherwise themaximum allowed number of TPM candidates is set based on the firstsyntax element.

At (S1830), when a current coding block in the set of coding blocks iscoded in a triangular prediction mode, a triangular prediction candidatelist of the current coding block is constructed based on a number of TPMcandidates, the number of TPM candidates on the triangular predictioncandidate list being less than or equal to the maximum allowed number ofTPM. The process (1800) proceeds to (S1899) and terminates at (S1899).

V. Computer System

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 19 shows a computersystem suitable for implementing certain embodiments of the disclosedsubject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 19 for the computer system are exemplary innature and are not intended to suggest any limitation as to the scope ofuse or functionality of the computer software implementing embodimentsof the present disclosure. Neither should the configuration ofcomponents be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of the computer system.

The computer system may include certain human interface input devices.Such a human interface input device may be responsive to input by one ormore human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1901), mouse (1902), trackpad (1903), touchscreen (1910), data-glove (not shown), joystick (1905), microphone(1906), scanner (1907), camera (1908).

The computer system may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1910), data-glove (not shown), or joystick (1905), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1909), headphones(not depicted)), visual output devices (such as screens (1910) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

The computer system can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1920) with CD/DVD or the like media (1921), thumb-drive (1922),removable hard drive or solid state drive (1923), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

The computer system can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1949) (such as, for example USB ports of thecomputer system; others are commonly integrated into the core of thecomputer system by attachment to a system bus as described below (forexample Ethernet interface into a PC computer system or cellular networkinterface into a smartphone computer system). Using any of thesenetworks, computer system can communicate with other entities. Suchcommunication can be uni-directional, receive only (for example,broadcast TV), uni-directional send-only (for example CANbus to certainCANbus devices), or bi-directional, for example to other computersystems using local or wide area digital networks. Certain protocols andprotocol stacks can be used on each of those networks and networkinterfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1940) of thecomputer system.

The core (1940) can include one or more Central Processing Units (CPU)(1941), Graphics Processing Units (GPU) (1942), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1943), hardware accelerators for certain tasks (1944), and so forth.These devices, along with Read-only memory (ROM) (1945), Random-accessmemory (1946), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1947), may be connectedthrough a system bus (1948). In some computer systems, the system bus(1948) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1948),or through a peripheral bus (1949). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1941), GPUs (1942), FPGAs (1943), and accelerators (1944) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1945) or RAM (1946). Transitional data can be also be stored in RAM(1946), whereas permanent data can be stored for example, in theinternal mass storage (1947). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1941), GPU (1942), massstorage (1947), ROM (1945), RAM (1946), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture, and specifically the core (1940) can provide functionalityas a result of processor(s) (including CPUs, GPUs, FPGA, accelerators,and the like) executing software embodied in one or more tangible,computer-readable media. Such computer-readable media can be mediaassociated with user-accessible mass storage as introduced above, aswell as certain storage of the core (1940) that are of non-transitorynature, such as core-internal mass storage (1947) or ROM (1945). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1940). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1940) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1946) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1944)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

JEM: joint exploration modelVVC: versatile video codingBMS: benchmark set

MV: Motion Vector HEVC: High Efficiency Video Coding SEI: SupplementaryEnhancement Information VUI: Video Usability Information GOPs: Groups ofPictures TUs: Transform Units, PUs: Prediction Units CTUs: Coding TreeUnits CTBs: Coding Tree Blocks PBs: Prediction Blocks HRD: HypotheticalReference Decoder SNR: Signal Noise Ratio CPUs: Central Processing UnitsGPUs: Graphics Processing Units CRT: Cathode Ray Tube LCD:Liquid-Crystal Display OLED: Organic Light-Emitting Diode CD: CompactDisc DVD: Digital Video Disc ROM: Read-Only Memory RAM: Random AccessMemory ASIC: Application-Specific Integrated Circuit PLD: ProgrammableLogic Device LAN: Local Area Network

GSM: Global System for Mobile communications

LTE: Long-Term Evolution CANBus: Controller Area Network Bus USB:Universal Serial Bus PCI: Peripheral Component Interconnect FPGA: FieldProgrammable Gate Areas

SSD: solid-state drive

IC: Integrated Circuit CU: Coding Unit HMVP: History-based MVP

MVP: Motion vector predictor

TMVP: Temporal MVP

TPM: Triangular prediction modeVTM: Versatile test model

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method of video decoding in a decoder,comprising: receiving a coded video bit stream; setting a maximumallowed number of triangular prediction mode (TPM) candidates for a setof coding blocks based on whether the coded video bit stream includes afirst syntax element that indicates a maximum allowed number of TPMcandidates; and when a current coding block in the set of coding blocksis coded in a triangular prediction mode, constructing a triangularprediction candidate list of the current coding block in the set ofcoding blocks based on a number of TPM candidates, the number of TPMcandidates on the triangular prediction candidate list being less thanor equal to the maximum allowed number of TPM candidates.
 2. The methodaccording to claim 1, wherein the coded video bit stream includes thefirst syntax element only when a maximum allowed number of mergecandidates is greater than or equal to
 2. 3. The method according toclaim 1, wherein the setting comprising: setting the maximum allowednumber of TPM candidates to 0 based on the first syntax element notbeing included in the coded video bit stream.
 4. The method according toclaim 1, wherein the coded video bit stream includes a second syntaxelement, the second syntax element indicating a difference between amaximum allowed number of merge candidates and the maximum allowednumber of TPM candidates, and the setting includes setting the maximumallowed number of TPM candidates based on a subtraction of thedifference between the maximum allowed number of merge candidates andthe maximum allowed number of TPM candidates from the maximum allowednumber of merge candidates.
 5. The method according to claim 1, whereinthe maximum allowed number of TPM candidates is less than or equal to amaximum allowed number of merge candidates.
 6. The method according toclaim 1, wherein the setting comprises: setting the maximum allowednumber of TPM candidates to a maximum allowed number of merge candidatesbased on the first syntax element not being included in the coded videobit stream.
 7. The method according to claim 4, wherein the maximumallowed number of TPM candidates either equals to 0, or is an integerfrom 2 to the maximum allowed number of merge candidates.
 8. The methodaccording to claim 1, wherein the maximum allowed number of TPMcandidates is determined to be 0 and the triangular prediction mode isnot applied to the set of coding blocks based on a second syntax elementindicating a difference between a maximum allowed number of mergecandidates and the maximum allowed number of TPM candidates is notincluded in the coded video bit stream.
 9. The method according to claim1, wherein the current coding block is coded in the TPM only when themaximum allowed number of TPM candidates is greater than or equal to apredetermined number N, where N is a positive integer.
 10. The methodaccording to claim 1, wherein when the maximum allowed number of TPMcandidates is greater than 0, the coded video bit stream includes athird syntax element that indicates a first index of the triangularprediction candidate list and a fourth syntax element that indicates asecond index of the triangular prediction candidate list, a maximumnumber of the first index equals to the maximum allowed number of TPMcandidates minus one, and a maximum number of the second index equals tothe maximum allowed number of TPM candidates minus two.
 11. Anapparatus, comprising: processing circuitry configured to: receive acoded video bit stream; set a maximum allowed number of triangularprediction mode (TPM) candidates for a set of coding blocks based onwhether the coded video bit stream includes a first syntax element thatindicates a maximum allowed number of TPM candidates; and when a currentcoding block in the set of coding blocks is coded in a triangularprediction mode, construct a triangular prediction candidate list of thecurrent coding block in the set of coding blocks based on a number ofTPM candidates, the number of TPM candidates on the triangularprediction candidate list being less than or equal to the maximumallowed number of TPM candidates.
 12. The apparatus according to claim11, wherein the coded video bit stream includes the first syntax elementonly when a maximum allowed number of merge candidates is greater thanor equal to
 2. 13. The apparatus according to claim 11, wherein theprocessing circuitry is further configured to set the maximum allowednumber of TPM candidates to 0 based on the first syntax element notbeing included in the coded video bit stream.
 14. The apparatusaccording to claim 11, wherein the coded video bit stream includes asecond syntax element, the second syntax element indicating a differencebetween a maximum allowed number of merge candidates and the maximumallowed number of TPM candidates, and. the processing circuitry isfurther configured to set the maximum allowed number of TPM candidatesbased on a subtraction of the difference between the maximum allowednumber of merge candidates and the maximum allowed number of TPMcandidates from the maximum allowed number of merge candidates.
 15. Theapparatus according to claim 11, wherein the maximum allowed number ofTPM candidates is less than or equal to a maximum allowed number ofmerge candidates.
 16. The apparatus according to claim 11, wherein theprocessing circuitry is further configured to set the maximum allowednumber of TPM candidates to a maximum allowed number of merge candidatesbased on the first syntax element not being included in the coded videobit stream.
 17. The apparatus according to claim 14, wherein the maximumallowed number of TPM candidates either equals to 0, or is an integerfrom 2 to the maximum allowed number of merge candidates.
 18. Theapparatus according to claim 11, wherein the maximum allowed number ofTPM candidates is determined to be 0 and the triangular prediction modeis not applied to the set of coding blocks when a second syntax elementindicating a difference between a maximum allowed number of mergecandidates and the maximum allowed number of TPM candidates is not‘included in the coded video bit stream.
 19. The apparatus according toclaim 12, wherein when the maximum allowed number of TPM candidates isgreater than 0, the coded video bit stream includes a third syntaxelement that indicates a first index of the triangular predictioncandidate list and a fourth syntax element that indicates a second indexof the triangular prediction candidate list, a maximum number of thefirst index equals to the maximum allowed number of TPM candidates minusone, and a maximum number of the second index equals to the maximumallowed number of TPM candidates minus two.
 20. A non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding causes the computer to perform a method, themethod comprising: receiving a coded video bit stream; setting a maximumallowed number of triangular prediction mode (TPM) candidates for a setof coding blocks based on whether the coded video bit stream includes afirst syntax element that indicates a maximum allowed number of TPMcandidates; and when a current coding block in the set of coding blocksis coded in a triangular prediction mode, constructing a triangularprediction candidate list of the current coding block in the set ofcoding blocks based on a number of TPM candidates, the number of TPMcandidates on the triangular prediction candidate list being less thanor equal to the maximum allowed number of TPM candidates.